Hydroformylation reactions involve the preparation of oxygenated organic compounds by the reaction of carbon monoxide and hydrogen (i.e., synthesis gas) with carbon compounds containing olefinic unsaturation. The reaction is typically performed in the presence of a carbonylation catalyst and results in the formation of compounds, for example, aldehydes, which have one or more carbon atoms in their molecular structure than the starting olefinic feedstock. By way of example, higher alcohols may be produced by hydroformylation of commercial C.sub.6 -C.sub.12 olefin fractions to an aldehyde-containing oxonation product, which on hydrogenation yields the corresponding C.sub.7 -C.sub.13 saturated alcohols. The crude product of the hydroformylation reaction will contain catalyst, aldehydes, alcohols, unreacted olefin feed, synthesis gas and by-products.
A variety of transition metals catalyze the hydroformylation reaction, but only cobalt and rhodium carbonyl complexes are used in commercial plants. The reaction is highly exothermic, i.e., the heat release is approximately ca 125 kJ/mol (30 kcal/mol). The position of the formyl group in the aldehyde product depends upon the olefin type, the catalyst, the solvent, and the reaction conditions. Reaction conditions have some effect and, with an unmodified cobalt catalyst, the yield of straight chain product from a linear olefin is favored by higher carbon monoxide partial pressure. In the hydroformylation of terminal olefinic hydrocarbons, the use of a catalyst containing selected complexing ligands, e.g., tertiary phosphines, results in the predominant formation of the normal isomer.
In commercial operation, the aldehyde product is typically used as an intermediate which is converted by hydrogenation to an alcohol or by aldolization and hydrogenation to a higher alcohol. The aldol-hydrogenation route is used primarily for the manufacture of 2-ethylhexanol from propylene that is converted to n-butyraldehyde.
Much research in the past 25 years has been directed to improving reaction selectivity to the linear product. Introduction of an organophosphine ligand to form a complex, e.g., Co(CO).sub.6 [P(n-C.sub.4 H.sub.9).sub.3 ].sub.2, significantly improves the selectivity to the straight-chain alcohol.
Recent developments of low pressure rhodium catalyst systems have been the subject of a considerable body of patent art and literature, and rhodium-triphenyl phosphine systems have been widely, and successfully, used commercially for the hydroformylation of propylene feedstocks to produce butyraldehyde.
Homogeneous catalysts formed from ligated metal atoms can perform very selective chemistries with high turnover rates. For example, rhodium complexes containing phosphine ligands have ideal properties as catalysts in the hydroformylation process used in making long chain aldehydes because of their propensity to form the linear rather than branched isomers. The linear aldehydes which can be formed with rhodium catalyst complexes are needed for formulating biodegradable detergents, plasticizers, specialty polymers, etc. Homogeneous rhodium catalyst complexes have a unique role in this chemistry in that they can take a linear terminal olefin and convert it into a predominantly linear aldehyde.
A typical homogeneous rhodium complex catalyst is formed with triphenylphosphine ligands in the presence of carbon monoxide and hydrogen. The rhodium bonds to the triphenylphosphine ligand through a phosphorous atom. A large number of complexes are formed between rhodium, triphenylphosphine, hydrogen, and carbon monoxide, because they form loosely bound molecular species which are involved in multiple equilibria as they dissociate and recombine with ligands in solution. One of the complexes can be a very active catalyst for the hydroformylation reaction which converts linear olefins into the next higher carbon number linear aldehydes by the addition of carbon monoxide and hydrogen. In addition, the catalyst converts some of the product aldehyde to dimer and trimer condensation products. The isomerization activity of the catalyst in extremely undesirable in applications designed to produce long chain linear aldehydes. Linear aldehydes containing between 12 to 15 carbon are readily hydrogenated to linear alcohols which are premium products for formulating biodegradable liquid detergents.
Others have synthesized high molecular weight phosphine ligands for use as homogeneous catalysts. High molecular weight polymeric phosphine ligands are synthesized by reacting polyvinylchloride, polychloroprene or brominated polystyrene with lithium diphenylphosphide at 20.degree. C. to 25.degree. C. These homogeneous catalysts containing bulky ligands are thought to be more easily separated from the reaction products by ultrafiltration. See Imyanitov et al., All-Union Scientific Research Institute of Petrochemical Processes, Neftekhimiya, 32, No. 3:200-7 (May-June 1992).
One conventional rhodium ligand used in the hydroformylation of higher .alpha.-olefins, such as 1-dodecene in an aqueous emulsion catalytic process, is sodium p-diphenyl phosphino benzoate, i.e., Ph.sub.2 P(p-C.sub.6 H.sub.4 COO.sub.3 Na). As discussed in Great Britain Patent Application No. 2,085,874, filed on Aug. 21, 1981, this rhodium ligand complex is active at low temperature and pressure, and gives a high selectivity to the normal isomer.
Still others have synthesized a rhodium ligand complex using a Ph.sub.2 P(m-C.sub.6 H.sub.4 SO.sub.3 Na) ligand as shown in Ahrland et al., "The relative Affinities of Coordinating Atoms for Silver Ion. Part II..sup.1 Nitrogen, Phosphorus, and Arsenic..sup.2 :, Chemical Society, 1958, pp. 276-288. The Ph.sub.2 P(m-C.sub.6 H.sub.4 SO.sub.3 Na) ligand was synthesized by slowly adding 10 grams of triphenylphosphine, with cooling, to a mixture of 20% SO.sub.3 --H.sub.2 SO.sub.4 (19 c.c.) and 65% SO.sub.3 --H.sub.2 SO.sub.4 (1 c.c.). The phosphine dissolved and the solution was heated on a water bath. The solution was tested at intervals by adding one drop to water (2-3 c.c) until a test drop gave a clear or only slightly cloudy aqueous solution (1-2 hours depending on the acid strength). The acid solution was cooled, poured cautiously into water (200 c.c.) and neutralized with saturated sodium hydroxide solution. The product separated as fine, white shining leaves.
As demonstrated in comparative Example 3, the sodium m-diphenyl phosphino benzene sulfonate (i.e., Ph.sub.2 P(m-C.sub.6 H.sub.4 SO.sub.3 Na)) ligand which was synthesized by direct sulfonation of triphenyl phosphine resulted in very low rates of reaction in the hydroformylation of 1-decene and a low selectivity to the desired normal isomer compared to the corresponding para substituted carboxylic or sulfonic acid ligands.
Sodium p-diphenyl phosphino sulfonate, i.e., Ph.sub.2 P(p-C.sub.6 H.sub.4 SO.sub.3 Na), was first synthesized by H. Schindlbauer (see H. Schindlbauer, Monatsh Chem, 96 (6), 1965, pp. 2051) from potassium diphenyl phosphide and p-chloro sodium benzoate by boiling at 67.degree. C. in tetrahydrofuran (THF) for 24 hours. This article describes the formation of a by-product, p-diphenyl phosphino benzene, i.e., Ph.sub.2 P(p-C.sub.6 H.sub.4 PPh.sub.2), resulting from displacement of the sulfonic group by the diphenyl phosphino group, but gives no yield for the sulfonic salt, i.e., Ph.sub.2 P(p-C.sub.6 H.sub.4 SO.sub.3 Na), which was identified by elemental analysis for phosphorus and sulfur but could not be recrystallized due to poor solubility.
The present inventors have discovered that by using a lithium salt of the p-chloro benzene sulfonic acid, i.e., Cl(p-C.sub.6 H.sub.4 SO.sub.3 Li) in a reaction with potassium diphenyl phosphide enables the isolation and purification of the product compound in high yield and purity. Since the lithium salt is more soluble then the corresponding sodium salt in THF, the reaction proceeds in 0.5 hours in boiling THF which is substantially faster than the formation of Ph.sub.2 P(p-C.sub.6 H.sub.4 SO.sub.3 Na) from Cl(p-C.sub.6 H.sub.4 SO.sub.3 Na). Moreover, the potassium salt (Ph.sub.2 P(p-C.sub.6 H.sub.4 SO.sub.3 K)) of the ligand as a result of a lithium/potassium salt exchange is obtained in an approximate yield of 50%. Also, the potassium salt of the ligand was found to be less soluble in organic solvents then the conventional sodium salts, such that it was able to be recrystallized from EtOH. The potassium salt was identified by elemental analysis, IR and P31 NMR.
Conventional hydroformylation reactions take place in an aqueous emulsion, such as that described in Great Britain Application No. 2,085,874, filed Aug. 21, 1981, in which the aqueous phase consists of a 1N NaHCO.sub.3 solution, thus generating an excess of sodium cations. Therefore, since the potassium ligand salt is soluble in water it is consequently exchanged "in situ" to the sodium salt. As such, when the Ph.sub.2 P(p-C.sub.6 H.sub.4 SO.sub.3 K) ligand complexed catalyst is used to hydroformylate 1-decene it exhibits comparable rates of conversion to both Ph.sub.2 P(p-C.sub.6 H.sub.4 SO.sub.3 Na) and Ph.sub.2 P(p-C.sub.6 H.sub.4 COO.sub.3 Na) ligands, and substantially higher rates of conversion than Ph.sub.2 P(m-C.sub.6 H.sub.4 SO.sub.3 Na).
The present invention also provides many additional advantages which shall become apparent as described below.